This invention relates to the fluidic flowmeter for measuring the flowrate of natural gas provided to a household and other gases.
The fluidic flowmeter is a flowmeter for measuring the flowrate by structuring a adhesion wall and a feed-back flow channel on a downstream side of a nozzle from which the fluid to be measured is blown out, generating a fluid vibration relative to the adhesions wall while utilizing the Coanda effect with the pressure propagation being transmitted to the feed back flow channel, and by designing the said fluid vibration (oscillation frequency) to be proportional to the fluid measured.
As the fluidic flowmeter with this type of structure, the flowmeters described in U.S. Pat. No. 3,640,133, U.S. Pat. No. 3,690,171, Japan Patent Official Disclosure No. 48-54962, Japan Patent Official Disclosure No. 53-77558, Japan Patent Official Disclosure No. 59-184822, etc. are already known to the public.
Because this fluidic flowmeter functions to blow out the measured fluid from the nozzle as described above for generating the fluid vibration, the flowrate of measured fluid being blown out of this nozzle must be stable in proportion to the flowrate as its essential condition, and a measurement error occurs if the flowmeter lacks such stability.
The flowrate of a fluid being blown out of the nozzle is governed greatly by the shape on an upstream side of the nozzle together with the shape of nozzle. For example, if there should be anything hindering the smooth flow in the flow channel on the upstream side of nozzle, a vortex flow appears to the fluid flowing into the nozzle, and this vortex flow exerts a great influence on the flowrate by a change in flowrate.
Therefore, as it can be understood from the aforesaid officially known fluidic flowmeters, that a straight flow channel is formed on the upstream side of the nozzle for making vortex flow unlikely.
Forming a straight flow channel on the upstream side of nozzle in this way is possible in a staged experiment room or at wide installation conditions. However, if a compact size is required from the installation condition like the gas meter of gas being supplied to general households, for example, through piping, it is impossible to form a sufficient straight flow channel on the upstream side of nozzle. Moreover, in the case of this type of gas meter, the valves and governors are frequently installed on the upstream side of the nozzle, and there also exist bends of piping or the land, offset by joints, all of which become factors causing vortex flow in the gas flow and exerting influence on the stability of the flowrate